A fundamental problem in cooling/freezing alimentary bodies, i.e. products intended as food for human beings or animal fodder, is that the transferred thermal effect per surface unit from the alimentary body to a gas flow enveloping the alimentary body will be low at low gas flow rates. In order to transfer large thermal effects, high gas flow rates are required, which implies that a large air flow will be necessary. At the same time, however, the temperature rise in the air will be slight. The large flow entails that cooling/freezing will be expensive and, in consequence of the slight temperature rise, the energy in the heated air can seldom be utilized.
Depending on, among other things, the feeding temperature of the alimentary bodies, their consistency, thickness etc., variations in transit time must be foreseen in order to achieve the desired outlet temperature of the alimentary bodies. The transmit time, i.e. the time during which the alimentary bodies are present in the cooling/freezing chamber, is generally controlled by the feed rate of the product flow, so that a low feed rate result in a longer transmit time than a high feed rate would.
It is previously known from V. B. Repin, "Heat exchange of a cylinder with low-frequency oscillations", Zhurnal Prikladnoi Mehaniki i Tekhnicheskoi, No. 5, pp. 67-72, September-October 1981, that heat transmission may be improved by generating a sonic field in the liquid. It is also previously known that it is advantageous if such a sonic field is of low frequency.
It will be obvious from the two parameters sound pressure and particle velocity in a sonic field that it is the particle velocity which provides the enforced heat transmission. It is also obvious that the heat transmission increases with increasing particle velocities. The reason why the prior-art method of employing low-frequency sound for heating or cooling of bodies has not hitherto enjoyed any practical importance is that there have not been any usable method or apparatus for generating sound with a sufficiently high particle velocity throughout the entire surface of the body intended to be cooled, or alternatively, heated.